cell communication and signal transduction, homeostasis and feedback Flashcards
direct contact
communication through cell junctions
signaling substances and other material dissolved in the cytoplasm can pass freely between adjacent cells
animal cells direct contact
gap junctions
plant cells direct contact
plasmodesmata
direct contact example
immune cells
antigen presenting cells (APCs) communicate to T cells through direct contact
local regulators
a secreting cell will release chemical messages (local regulators/ligands) that travel a short distance through extra cellular fluid
chemical messages will cause a response in a target cell
local regulators examples
paracrine signaling
synaptic signaling
paracrine signaling
secretory cells release local regulators (ie growth factors) via exocytosis to an adjacent cell
synaptic signaling
occurs in animal nervous systems
neurons secrete neurotransmitters and they diffuse across the synaptic cleft (space between the cell and target cell)
(can be considered long distance signaling depending on the length of the neuron)
long distance signaling
animals and plants use hormones for long distance signaling
long distance signaling in plants
plants release hormones that travel in the plant vascular tissue (xylem and phloem) or through the air to reach target tissues
long distance signaling in animals
animals use endocrine signaling by which specialized cells release hormones into the circulatory system where they reach target cells
long distance signaling example
insulin
insulin is released by the pancreas into the bloodstream where it circulated through the body and binds to target cells
three stages of cell-to-cell messages
1- reception
ligand binds to receptor
2- transduction
signal is converted
3- response
a cell process is altered
reception
the detection and receiving of a ligand by a receptor in the target cell
receptor
macromolecule that binds to a signal molecule (ligand)
all receptors have an area that interacts with the ligand and an area that transmits a signal to another protein
what happens when the ligand binds to the receptor?
allows the receptor to interact with other cellular molecules and initiated transduction signal
plasma membrane receptors bind to ligands that are
polar, water-soluble
large
plasma membrane receptors examples
G protein coupled receptors (GPCRs)
ligand-gated ion channels
where are intracellular receptors found?
the cytoplasm or nucleus of target cells
intracellualr receptors bind to ligands that
can pass through the plasma membrane (ie hydrophobic molecules)
steroid and thyroid hormones
gases like nitric oxide
transduction
the conversion of an extra cellular signal to an intracellular signal that will bring about a cellular response
requires a sequence of changes in a series of molecules known as a signal transduction pathway
signal transduction pathway regulates protein activity through
phosphorylation by the enzyme protein kinase, which relays signal inside cell
dephosphorylization by the enzyme phosphatase, which shuts off pathways
second messengers
small, non-protein molecules and ions that help relay the message and amplify the response during transduction
common second messenger
cAMP (cyclic AMP)
response
the final molecule in the signaling pathway converts the signal to a response that will alter a cellular response
mutations to receptor proteins or to any component of the signaling pathway will result in a change to the blank of the signal
transduction
two important categories of cell membrane receptors in eukaryotic organism
G protein coupled receptors (GPCRs)
ion channels
GPCRs
important in animal sensory systems
bind to a G protein that can bind to a GTP (similar to ATP)
GPCR and G protein are inactive until ligand binding to GPCR on the extra cellular side
ligand binding causes cytoplasmic side to change shape and allows for the G protein to bind to GPCR (GPCR and G protein activate and GDP becomes GTP)
part of activated G protein can then bind to enzyme and activate it, amplifying signal and leads to a cellular response
ligand ion channels
located in plasma membrane
important in nervous system
when a ligand binds to the receptor, the “gate” opens or closes to allow diffusion of specific ions
set points
values for physiological conditions that the body tries to maintain
have a normal range for which it can fluctuate
homeostasis
state of relatively stable internal conditions
body maintains homeostasis through
feedback loops
two types of feedback loops
positive and negative
stimulus
variable that will cause a response
receptor/sensor
sensory organs that detect a stimulus; this information is sent to the control center (brain)
effector
muscle or gland that will respond
response
changes (decreases or increases) the effect of the stimulus
negative feedback
reduces the effect of a stimulus
negative feedback examples
sweat
blood sugar
breathing rate
positive feedback
increases the effect of a stimulus
positive feedback examples
child labor
blood clotting
fruit ripening
disease
when the body is unable to maintain homeostasis
cell signaling as a means of homeostasis
in order to maintain homeostasis, the cells in a multicellular organism must be able to communicate
communication occurs through signal transduction pathways
